Hydrotreating of petroleum feedstocks and various boiling fractions thereof, has become increasingly important because of more stringent product quality requirements. Furthermore, the petroleum industry foresees the time when it will have to turn to relatively high boiling feeds derived from such materials as coal, tar sands, oil-shale, and heavy crudes. Feeds derived from such materials generally contain significantly more deleterious components, such as sulfur, nitrogen, oxygen, halides, and metals, Consequently, such feeds require a considerable amount of upgrading in order to reduce the content of such components, thereby making them more suitable for further processing, such as fluid catalytic cracking and/or catalytic reforming.
Hydrotreating is well known in the art and usually requires treating a hydrocarbonaceous feed with hydrogen, in the presence of a catalyst to effect conversion of at least a portion of the feed to lower boiling products, and/or removal of deleterious components. See for example U.S. Pat. No. 2,914,462 which discloses the use of molybdenum sulfide for hydrodesulfurizing gas oil and U.S. Pat. No. 3,148,135 which discloses the use of molybdenum sulfide for hydrorefining sulfur and nitrogen-containing hydrocarbon oils. Further, U.S. Pat. No. 2,715,603 discloses the use of molybdenum sulfide as a catalyst for the hydrogenation of heavy oils, while U.S. Pat. No. 3,074,783 discloses the use of molybdenum sulfides for producing sulfur-free hydrogen and carbon dioxide, wherein the molybdenum sulfide converts carbonyl sulfide to hydrogen sulfide. Molybdenum and tungsten sulfides have other uses as catalysts, including hydrogenation, methanation, water gas shift, etc. reactions.
In general, with molybdenum and other transition metal sulfide catalysts, as well as with other types of catalysts, greater catalyst surface areas generally result in more active catalysts than similar catalysts with lower surface areas. Thus, those skilled in the art are constantly trying to achieve catalysts having ever greater surface areas. More recently, it has been disclosed in U.S. Pat. Nos. 4,243,553 and 4,243,554 that molybdenum sulfide catalysts of relatively high surface area may be obtained by thermally decomposing selected thiomolybdate salts at temperatures ranging from about 300.degree.-800.degree. C. in the presence of essentially inert, oxygen-free atmospheres. Suitable atmospheres are disclosed as consisting of argon, a vacuum, nitrogen, and hydrogen. In U.S. Pat. No. 4,243,554, an ammonium thiomolybdate salt is decomposed at a rate in excess of 15.degree. C. per minute, whereas in U.S. Pat. No. 4,243,553, a substituted ammonium thiomolybdate salt is thermally decomposed at substantially slower heating rate of about 0.5 to 2.degree. C./min. The processes disclosed in these patents are claimed to produce molybdenum disulfide catalysts having superior properties for water gas shift and methanation reactions as well as for catalyzed hydrogenation and hydrotreating reactions.
Hydrotreating catalysts comprising molybdenum sulfide, in combination with other metal sulfides, are also known. For example, U.S. Pat. No. 2,891,003 discloses an iron-chromium composition for desulfurizing olefinic gasoline fractions. Further, U.S. Pat. No. 3,116,234 discloses Cr-Mo and also Mo with Fe and/or Cr and/or Ni for hydrodesulfurization. Also U.S. Pat. No. 3,265,615 discloses Cr-Mo for hydrodenitrogenation and hydrodesulfurization.
Hydrotreating catalysts can also be used in a multi-stage process or in a stacked-bed process. For instance, U.S. Pat. No. 4,392,945 discloses a hydrodesulfurization process by using a two-stage reactor system with interstage removal of H.sub.2 S and NH.sub.3. The first stsage reactor contains a Ni-promoted conventional catalyst, while the second stage reactor contains a Co-promoted conventional catalyst. U.S. Pat. No. 4,534,852 discloses a stacked-bed process. The catalyst in the upstream zone contains phosphorus in the range of 2-4 wt% and is a Ni-promoted Mo sulfide catalyst. The catalyst in the downstream zone has a phosphorus level of less than 0.5 wt% and is an Mo sulfide catalyst promoted by Co and/or Ni. Both catalysts are supported on a carrier consisting mostly of alumina and are prepared via conventional techniques. This stacked-bed process is primarly applicable to resids hydrotreating wherein catalyst deactivation by metals and coke is a primary process concern.
More recently, new classes of hydrotreating catalysts have been developed which comprise self-promoted molybdenum and/or tungsten sulfide. For example, U.S. Pat. No. 4,663,023, which is incorporated herein by reference, teaches the catalysts represented by the formula MM'A.sub.x where M is one or more promoter metals such as Ni and Co; M' is Mo and/or W; x is a number 1 to 5, and A is oxygen or sulfur. These catalysts are prepared from a precursor represented by ML(Mo.sub.y W.sub.1-y A.sub.4) wherein M is one or more promoter metals, L is one or more, neutral, nitrogen-containing ligands at least one of which is a chelating polydentate ligand; and y is any value from 0 to 1, and A is O or S. These precursors are also taught in U.S. Pat. No. 4,595,676, which is also incorporated herein by reference. Other precursors and taught in U.S. Pat. Nos. 4,591,429; 4,632.747; and 4,668,376 all of which are incorporated herein by reference. Further, chromium-molybdenum and tungsten sulfide catalysts are taught in U.S. Pat. Nos. 4,622,128; 4,626,339; and 4,716,139, all of which are also incorporated herein by reference.